Patent GB-561674-A (GB)
Title: Improvements in methods of colour correction in colour photography
IPC: G03C7/18
Filed: 1942-09-03
Abstract: 561,674. Colour photography. KODAK, Ltd. (Eastman Kodak Co., and Dearing, L. M.). Sept. 3, 1942, No. 12456. [Class 98 (ii)] In the production on material having on a single support red-, green- and blue-sensitive emulsions of a subtractive three-colour record having an integral mask from a coloured original, at least one other emulsion in a separate layer on the same support is simultaneously exposed to light of one or two of the three primary colours coming from the coloured original to form a latent masking image or images, and the latent colour component images are processed to subtractively coloured images and the latent masking image or images to an image or images of complementary light value of lower maximum density and preferably of lower gamma. The additional emulsion may be sensitized to red or green or to both, or two emulsions may be used, one sensitized to red and the other to .green, or one to red and the other to red and green, or one to green and the other to red and green, or both to red and green. The masking emulsion may be sensitive only to blue. The masking image or images may be developed to silver or to dye, e.g. by colour development, including a neutral grey dye image. The emulsions containing the colour component images may be coated in one, two, or three' layers. The emulsion or emulsions for the masking image or images may contain colour couplers for producing coloured or neutral grey images by colour development. Alternatively, the picture emulsions may contain colour couplers and the masking images no couplers. As shown in Fig. 1, multilayer material is processed by reversal to a subtractively coloured positive in which an integral mask is also formed. The positive may be copied by contact or projection on to multilayer material (in which an integral mask may also be formed) or on to separate' emulsions. The colour and nature of the mask in the first material may be such as to correct only' for deficiencies in the first multicolour image or in both the first and second multicolour images. The cellulose ester or like support 10 carries a red-sensitive emulsion layer 11 containing a colour coupler for producing a masking image and red-, green- and blue-sensitive emulsion layers 12, 13 and 14. The layer 12 is sensitized with 3: 3<1>- dimethyl-9-ethyl-4 : 5 : 41 : 5<1>-dibenzthiacarbocyanine chloride, and the layer 13 with 1 : 3<1>- diethyl-4 : 5-benzthia-2<1>-cyanine bromide. The couplers may be incorporated by the methods' of Specifications 524,554, 524,555, or 541,589. The yellow filter layer 15 js provided between the blue- and green-sensitive emulsions. The coupler in the layer 11 may be 2 : 4-dichloro-1- naphthol, 1 : 5-dihydroxynaphthalene, or pbenzylphenol. The red-sensitizer in layer 11 may be pinacyanol, which is destroyed in the first development, and the emulsion has a higher blue speed. After exposure, the film is developed in a developer comprising sodium sulphite, sodium hydroxide, 2-amino-5-diethylaminotoluene hydrochloride, and metol to give a purple or neutral grey masking image and silver images in layers 12, 13 and 14, which layers are then processed to colour as described in Specification 507,841. Alternatively, after exposure, the film may be developed first in a colour developer and then in a black-and-white developer. The negative masking image can be of any colour provided a complementary coloured filter is used in the printing beam. If the masking image is processed to neutral grey, it compensates for undesired blue and green absorptions in the cyan image ; if to magenta, for the undesired absorption of green by the cyan dye ; and if to yellow for the undesired absorption of blue by the cyan dye. If the masking layer 11 were green-sensitive, the masking image would compensate for undesired absorption by the magenta image and could be coloured yellow or cyan. If sensitive to both red and green (not necessarily equally sensitive), it would compensate for undesired absorptions in both the cyan and magenta images. In modifications, colour development of the residual silver halide in the masking layer is prevented by the following means :-(1) the layer 11 may be given an additional colour sensitivity (e.g. to infra-red or deep ultra-violet or even to green if layer 12 is not green-sensitive and the green-sensitivity of layer 13 does not survive first development), that survives the first negative development, and after such development layer 11 is exposed uniformly to the appropriate light and the re-exposed silver halide therein developed to silver ; (2) the layer 11 may contain a colour coupler (e.g. an ester of a soluble coupler broken down by alkali subsequent to negative development, a coupler having an aldehyde group such as a hydroxybenzaldehyde which can be solubilized by strong bisulphite, solutions, or an alkali-soluble coupler 'incorporated by the method 'of Specification 524,554 or Specification 524,555) which can be broken down in the unexposed areas during or after first development so that it can be removed by treatment not affecting the layers 12, 13 and 14, and after removal of the coupler the unexposed silver halide is exposed with light to which it is most sensitive (e.g. infra-red or ultra-violet), the silver image developed, and after treatment of the other layers' both silver images are removed in the final removal of silver ; (3) the,layer 11 may contain an easily saponifiable ester of a leuco dye or a leuco base intermediate of a dye, e.g. leuco - indophenols. or leuco - indamines, the residue of which may be removed from the masking layer after development of the negative dye image therein ; (4) the layer 11 consists of a fine-grain silver chloride emulsion and after negative development the residual silver chloride is removed with strong alkali metal sulphite. solution, the layer 11 being then placed close to the yellow filter layer, i.e. between layers 13 and 15 or between layers 13 and 14, layer 15 being dispensed with, if the filter dye is incorporated in layer 11 and the other layers being slow-speed emulsions.; or (5) the layer 11 consists of a coarse-grain silver iodide emulsion which develops only in a strong negative developer and not in a weak colour developer. The masking layer may be provided on the back of the support and an anti-halation layer coated above it. In this case the masking image may be toned. Material designed for the negative-positive process, shown in Fig. 2, comprises a support 10 carrying a red-sensitive emulsion 24, a green-sensitive emulsion' 25, a thin red-sensitive emulsion layer 26 having an' additional sensitivity to infra-red or ultra-violet and designed to receive a masking image, a yellow filter layer 15, and a blue-sensitive emulsion 27, layers 24, 25 and 27 containing couplers giving cyan, magenta, and yellow dyes on colour development. After 'exposure, the material is colour developed, the residual silver halide, in the masking layer is exposed to infrared or ultra-violet and developed in a lowcontrast developer containing a coupler to produce a red, orange, or neutral/grey dye image, e.g. a developer including 2-amino-5-diethylaminotoluene hydrochloride, KCNS, and 6- nitrobenzimidazole and containing as coupler cyanacetanilide, or a neutral grey developer including 2-amino-5-diethylaminotoluene hydrochloride, KCNS, NaOH, and p-benzylphenol, and the negative silver images removed by bleaching and fixing. The masked colour negative is then printed on to similar material having no masking layer. The material may be processed to a positive by reversal colour development, and in this case an autopositive red- or green-sensitive emulsion containing a coupler is used for layer 26, which in this case may be placed on the back of the support. In the negative-positive process with a masking layer on the back of the support, after exposure and colour development,- the silver masking image is converted to silver iodide or a similar compound by local application of a suitable solution or toned to any other image (e.g. gold, uranium, or Prussian Blue) which will stand silver bleaching and fixing solutions. Mixed dye images may be formed in a masking layer by incorporation of more than one colour coupler. Specifications 501,661, 512,559, 512,608, 516,514, 516,816, 517,416, 524,154, 540,445, 541,298, 541,771, 547,519, 553,196, 553,229 and 553,230 are also referred to. The Provisional Specification refers also to material without a separate masking layer in which the silver halide to receive the masking exposure is incorporated in one of the colour component emulsion layers. The masking dye image may be less stable in acid or alkaline solutions than the component dye images go that if desired it may be removed. The colour coupler may be so chosen that the masking dye image may be removed by weakly acid, strongly basic, or moderately reducing or oxidizing baths. The layer 11 may consist of a fast red-sensitive autopositive emulsion with or without additional sensitivity in the infra-red or ultraviolet and not containing a colour coupler.